Effect of Supercritical CO2 on Mechanical Properties of Tight Carbonate Rocks
The supercritical CO2 fracturing has the characteristics of low fracture pressure and easy formation of complex fractures in tight carbonate rock,but the mechanical mechanism of the effect of supercritical CO2 on tight carbonate rocks is not clear.The physical properties,acoustic response,rock mechanical properties and fracture morphology of the tight dolomite samples from Majiagou Formation were studied by using the high temperature and high pressure supercritical CO2 saturated fluid method,namely the samples were immersed in supercritical CO2+formation water for different time.The results show that with the increase of soaking time,the dissolution pore size and the porosity and permeability of the rock sample increase due to chemical corrosion,and the corresponding acoustic velocity,dynamic and static rock mechanical parameters all decrease.When the soaking time is longer than 1.0 d,the physical property parameters of the rock sample increase and the mechanical strength decreases obviously.With the increase of soaking time,the fracture morphology of rock samples develops from single low angle shear joint to high angle shear joint,conjugate joint and shear and tension composite joint.In short fracturing time(≤ 1.0 d),the weak acid formed by supercritical CO2+formation water has limited deterioration degree to rock mechanical strength.
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